Wait! Please do not mark this as a duplicate until you have read this entire question. I know full well there is supposed to be a highly upvoted solution here but it is problematic because there have been many important changes to windows since the question was first answered. Some of these changes completely invalidate aspects of the solution (for example see ramhound's first comment in this question here). Also there are now 27 comments below the top answer so any additional comments are unlikely to be read.
So now my question: I wish to prevent windows from rebooting after doing an update because sometimes I want to leave my PC performing a task unattended for up to a week at a time. Can it be done?
SOLUTION FOUND: Windows 10 Reboot Blocker:
A simple Windows-Service that will update this "active hours" timeslot
in the background.
It is free, simple and it works.
March 2019: Still no unwanted reboots.
March 24th 2019: Windows 10 reboot blocker has now been marked as the correct answer in the duplicate question.